Transformation and Re-transformation of a Western River: Variations in Channel and Floodplain Resilience Variables over 140 Years

The Middle Fork John Day River (MFJD) in northeastern Oregon is a typical western montane river affected by waves of development and re-development by Euro-American settlers, including gold mining, development of ranches, cattle grazing, timber harvest, railroad and road building and, more recently, river and floodplain restoration. We present conceptual models of the drivers, responses and interactions of the main land practices. Dredge mining for gold, for example, simplified channels and destroyed floodplain vegetation, but also created floodplain wetlands and increased floodplain woody vegetation. Land practices varied spatially among confined and unconfined reaches and public and private land ownership, and temporally over different periods of development. Communities and government agencies also evolved over time. We developed historical data for variables related to resilience within three broad categories: riparian vegetation, channel morphology and channel-floodplain connectivity. Shifts from woody to herbaceous riparian vegetation can affect water quality and riparian habitat. More complex channel morphology, as indicated by high sinuosity and secondary channels, is associated with more diverse aquatic and riparian habitat, and resilience to flood impacts. As an undammed river, the MFJD has longitudinal connectivity, but lateral connectivity has been influenced by roads and railroads, reducing hydrologic and ecological exchanges, and resilience to flood impacts. Changes these variables since the 1880s were quantified using data from early land surveys, maps, aerial imagery, field measurements, and spatial data on land ownership and management. We are unable to quantify social variables for resilience, but we describe potential social drivers and dampers of the biophysical changes. The results show that mining had spatially concentrated impacts, while ranch development was more gradual but spatially extensive. Early river restoration actions in some cases reduced resilience, and more recently, passive versus active restoration had different effects. This preliminary analysis, while incomplete, provides a context for evaluating the resilience impacts of past and future development strategies.